I. Field of the Invention
This invention relates generally to electrosurgical apparatus, and more particularly to a catheterlike device capable of being routed through the vascular system and having a first set of sensing electrodes for mapping ectopic foci within the myocardium and a second set of bipolar electrodes which may be used to ablate myocardial tissue to remove such ectopic foci.
II. Discussion of the Prior Art
Natural cardiac pacing, under normal circumstances, begins with depolarization of sinoatrial (S-A) node which spreads an electrical impulse from its location in the right atrium across to the left atrium and downward towards the ventricles. The depolarization wave reaches the transition zone between the atrium and the ventricles where the atrio-ventricular (A-V) node or junction is located. When this node fires, the impulse is passed down the Bundle of His, between the right and left ventricles, and into the right and left bundle branches, each branch supplying one ventricle. These bundle branches then divide into finer paths of conducting tissue which spread from the inner to the outer surfaces of the heart and which are referred to as the Purkinje fibers. These fibers feed the depolarization impulse into all portions of the ventricular myocardium. Certain tachyrhythmias can be traced to the existence of ectopic foci. For example, atrial tachycardia may result when an alternative pacemaker focus in the atrium, i.e., a focus other than the S-A node, fires at a higher rate than the S-A node. If the ectopic foci is in the ventricle, it may lead to ventricular tachycardia and more seriously to ventricular fibrillation.
A number of drugs are available for treating ventricular tachycardia and other ventricular arrhythmias, such as lidocaine, quinidine and procaineamide. Beta-blocking drugs, such as propranolol, may also be used where there is an excess of either sympathetic nervous activity or adrenal secretion.
Where drug therapy is ineffective to arrest episodes of lifethreatening tachyrhythmias, surgical procedures have been used to remove ectopic foci appearing in either or both of the atrium and ventricles. Generally, the surgical procedures have involved open heart surgery wherein a thoracotomy is required to gain access to the heart. An incision is made through the pericardium and the heart muscle is mapped to locate the sites of the ectopic foci. The involved myocardial tissue is then surgically removed, thereby replacing the excitable tissue with scar tissue. Open heart surgery is a relatively traumatic procedure requiring a prolonged period of hospitalization and a long period of recuperation.
Various cardiac procedures have been devised for treating a number of cardiac abnormalities in which a catheter is used to correct the defect. For example, stenotic lesions, accompanying coronary artery disease, are now routinely treated using balloon angioplasty. In this procedure, an elongated, flexible, plastic tube having an inflatable balloon at its distal end may be routed through the vascular system from a location on the patient's leg and when the balloon is appropriately positioned across the site of the lesion, an inflation fluid is injected through the lumen of the catheter to expand the balloon and thereby open up the clogged or partially clogged coronary blood vessel. In a valvuloplasty procedure, a catheter is again routed through the vascular system with the balloon being positioned in the valve to be treated. Upon inflation of the balloon, the calcified deposits binding the valve leaflets together is ruptured, restoring the flexibility to the valve tissues.